Temperature control is necessary for many laboratory specimens and is often critical for biological samples for which permanent changes in the sample integrity may occur when stored under improper conditions. While refrigeration and freezing are adequate solutions for temporary or archival storage, temperature management for samples becomes more challenging under conditions where the samples are in the open, as when being manipulated on the laboratory bench. Under these working conditions, biological samples are often maintained at lower temperatures between 0 degrees Celsius and 5 degrees Celsius by inserting the sample vessels into crushed ice. This practice, while effective in maintaining a reduced temperature, has multiple disadvantages including sample vessel instability and visual disarray as the ice melts, leading to sample spillage and loss, potential contamination of the sample, identification error, and exposure of the sample to elevated temperatures.
As an alternative to this method, thermo-conductive racks into which laboratory containers and tubes are inserted may be used in conjunction with ice to provide stability and organizational efficiency. Thermo-conductive racks can interface with alternative thermoregulatory devices, including phase transition gels, chemical heat packs, dry ice, liquid nitrogen, mechanically refrigerated devices, electric thermo-regulated devices, passive thermal masses and water baths. For applications that require temperatures below room temperature and portability, thermo-conductive racks can be used in conjunction with thermal reservoirs which can maintain a narrow temperature range by incorporating a material undergoing a phase transition of a substance from solid to liquid. Thermal regulators of this nature may comprise a phase transition medium enclosed in a plastic housing that is molded to a configuration that will receive the laboratory container tubes into recesses directly. Alternatively, thermal regulators may comprise a thermo-conductive rack typically constructed from a metal into which the container tubes are inserted and which serves to transmit environmental heat influx into the tubes directly to the phase change medium, which may be enclosed in a variety of containers (see the CoolRack™ line of products offered by Biocision LLC).
Thermo-conductive racks typically comprise a solid alloy block into which wells are introduced by machine operations for the purpose of receiving the sample vessels. This method of construction is cost-effective and highly functional under most working conditions. Limitations in solid alloy block construction become apparent for specific size ranges and operation conditions. Although thermo-conductive aluminum alloys have a relatively low density, for larger sample tubes or for larger sample arrays, the mass of the rack can exceed a comfortable handling limit for the operator. In addition, where the sample vessels are longer in length, sample rack height can extend above surrounding containment vessels such as ice buckets. Under this condition, air that is in contact with the elevated surface of the rack will cool and increase in density. The cool air in the absence of containment will flow downward and be replaced by air with a greater temperature. The continuous flow of warm air on the samples will place a substantial burden on the thermoregulatory device and increase the thermal gradient within the sample rack. Thermo-conductive racks can exhibit other undesirable properties during use, such as the collection of atmospheric condensate on the exterior surface at lower temperatures that may lead to local liquid water accumulation and degrade the secure grip friction properties of the tool.
Therefore, there is a need for a portable thermo-conductive laboratory sample rack that provides for the transfer of thermal energy to and from a sample vessel and a thermoregulatory device, that provides the temperature control properties of a solid thermally conductive rack, that has a reduced mass when compared to a thermally conductive rack of the same dimensions, and ideally has a means to reduce heat exchange with the environment. This invention meets these needs.